A METHOD OF DETECTING THE EARTH CONTENT IN BEETS

Abstract: A method of detecting the earth content in agricultural crops, such as beets, by measuring the gamma -radiation of the earth, the counting number of the measured gamma -radiation being corrected for differences in different types of earth. According to the invention this correction is performed by the counting number being corrected for the content in the earth of humus by utilizing that the content of humus is the primary factor influencing the counting number. The correction for the content of humus in the earth can be performed by a correction for the potassium content in the earth by utilizing that humus contains a particularly high amount of uranium compared to the amount of potassium. Furthermore it is possible to perform a correction for types of humus by means of a step function presenting a soft transition. As a result, the measuring is almost independent of the type of earth. In addition, the measuring can be performed in a relatively short period.

Description: Title: A method of detecting the earth content in beets Technical Field The invention relates to a method of detecting the earth content in agricultural crops, such as beets by a measuring of the 7-radiation of the earth, the counting number of the measured γ-radiations being corrected for differences in different types of earth. Background Art An article by P.G. Atherton i Annual Report Sugar Research Council (Australia) 1989/90 p. 58 describes an employment of the 7-radiation emitted by isotopes in the earth as a measurement of the earth content in sugar cain deliveries. Tests have shown that 0 to 5 % by weight of earth in the sugar cain deliveries can be determined with a statistic accuracy of 0.8% at the 95% confidence level. Based on measurements performed on 16 different earth types Atherton indicates that individual calibrations between 7-counting numbers and the earth percentage can be necessary because the earth types contain different amounts of isotopes. Brief Description of the Invention The object of the invention is to provide a simple method of correcting for the content of different isotopes in the earth. The method according to the invention is characterised by the counting number being corrected for the content in the earth of humus by utilizing that humus is the primary factor influencing the counting number. As a result it is very easy to compensate for the content of different isotopes in the earth, as nothing but the content of humus in the earth must be determined. Furthermore it is according to the invention possible to correct for the content of humus in the earth by compensating for the content of potassium in the earth by utilizing that humus contains a particularly high amount of uranium compared to the amount of potassium. The correction for the content of potassium may according to a first approxima- tion be performed by the counting number Int being corrected by the factor K/overK where Int is the counting number in almost the entire energy range, where K is the counting number in the range with the highest amount of potassium, and overK is the energy range thereabove. As a result, the variation of the measuring results is reduced. The correction can be improved by correcting for the type of humus by means of a step function preferably presenting a soft transition. As a result, the variation of the measuring results is further reduced. Brief Description of the Drawing The invention is explained in greater detail below with reference to the accom¬ panying drawings, in which Fig. 1 illustrates an apparatus for removing beet samples and detecting the earth content by the method according to the invention, Fig. 2 illustrates the average spectrum of energy for 20 earth samples, Fig. 3 illustrates the counting numbers of the different earth samples before and after the correction for the content of potassium, Fig. 4 illustrates the spectrum of energy for sample No. 2, Fig. 5 illustrates the spectrum of energy for sample No. 7, Fig. 6 illustrates the spectrum of energy for sample No. 15, Fig. 7 illustrates the counting numbers of the 20 earth samples after the correc¬ tion for the content of different types of humus, and Fig. 8 illustrates a step function for correcting for different types of humus. Best Mode for Carrying Out the Invention The apparatus shown in Fig. 1 comprises a plurality of boring tubes 1 to be bored into a load of beets on a lorry 2. Each tube 1 comprises a detector capable of measuring the γ-radiation from the earth in the beet load. As the different earth types emit different γ-radiations per mass unit, it is necessary to correct for the type of earth so as to obtain a sufficient accuracy. Radioactive substances (isotopes) in earth, such as uranium, potassium, and thorium emit γ-rays with different energies. The on-line measuring apparatus shown in Fig. 1 is used for measuring the earth percentage in loads of beets on a lorry 2. When the lorry 2 is stopped, a boring tube 1 is bored into the load of beets. The boring tube 1 comprises a detector measuring the γ-radiation from the earth in the load. After measuring for about 1 minute, the boring tube 1 is retracted and the beets are unloaded. The detector comprises an Nal-crystal. When this Nal-crystal meets a γ-quantum, said quan- tum may be absorbed by the Nal-crystal emitting a high or low amoimt of its energy. A γ-quantum emitted by the isotope potassium-40 contains for instance an energy of 1.46 MeN. The emission of such a quantum cannot therefore exceed 1.46 MeN. In connection with a partial absorption, the emitted energy is lower. Although the energy of the quantum is only partially absorbed, the remaining energy can nevertheless be absorbed by the Νal-crystal. When a quantum emits energy to the crystal, said emission involves emission of photons. The detector utilizes that the energy of the emitted photons depends in an unambiguous manner on the absorbed energy of the γ-quantum. When the emission of light from the Nal-crystal is quantitatively measured, it is possible to determine the energy absorbed from a γ-quantum. The measuring period can be almost halved by two boring tabes being used. The measuring apparatus, cf. Fig. 1 measures in 1024 channels corresponding to 1024 different energies. The energy is proportional to the channel number. Channel No. 1 corresponds to an energy of 3 KeV, and channel No. 1024 corre¬ sponds to an energy of 3.07 MeN. Reconsidering potassium-40 with an energy of 1.46 MeN, a high amount of this isotope in the material to be analyzed results in a peak in the spectrum of energy adjacent channel No. 487. This appears from Fig. 2 showing a spectrum of energy representing the average value of 20 differ¬ ent types of earth. The potassium peak appears in the spectrum adjacent channel No. 487. The very low energies matching channels 1 to 25 are very sensitive to noise. A noise peak appears on the channels 10 to 15. The very high peak adjac¬ ent channel 60 originates partly from isotopes emitting quanta in this energy range and partly from quanta of higher energies and only having released some of their energy to the Nal-crystal. Both uranium and thorium emit energy quanta of a low energy while decaying to elements of a lower number. The emission of quanta having released an amount of their energy corresponds, however, more or less to a large number of secondary energy emissions within the low energy range. In the beet load the detector is surrounded by a large amount of beets and earth. The background radiation is therefore very low compared to the radiation from the earth. In this manner an almost pure signal is received from the earth. The detector detects the signal in a spherical area inside the beet load, but as both beets and earth attenuate the γ-radiation, the radiations emitted by the earth closest to the detector are strongest. The area detected by the detector is con¬ sidered to be semi-infinite. When the density of the earth in the load is higher, the halving distance of the γ-radiation containing a specific energy is lower. Despite this fact, the number of quanta hitting the detector increases with the density of earth. If desired, it is possible to correct for background radiation. The total number of quanta transmitted in equally large time intervals from the same amount of earth increases in the order sand, sandy clay, and heavy clay. Heavy types of clay would transmit almost twice as many γ-quanta as sand without the background radiation. A utilization of the total number of transmitted γ-quanta per time unit as a direct measurement for the density of the earth in a beet load is therefore subject to a high uncertainty. The difference between sand and heavy clay is not only the total intensity, but the spectra differ too. The spectrum of each type of earth can be considered the finger-print of each type of earth. These finger-prints contain useful information. The low energies in the measured spectrum have to a certain degree been com¬ pensated for by partially absorbed quanta with higher energies and by secondary absorptions. The intermediary interval provide, however, so perfect measure¬ ments that they can be used for characterising the types of earth. In this manner it is possible to compensate for different radiations from different types of earth. The purer intervals of the spectrum with higher energies are not attractive due to the relatively low counting numbers in these intervals. The number of quanta transmitted by a radioactive source for equally long periods is substantially poison-distributed. It means that the variation of measured quanta corresponds to the square root of the average value. Low counting numbers present therefore a relatively large variation (variation/average value). The relative variation is inter¬ esting because the measuring technique is based on almost perfect measurements of the γ-radiation of the earth. Irrespective of corrections, the final number must in an unambiguous manner depend on the earth percentage. One of the most interesting isotopes in the spectrum of energy is potassium-40. A summarizing of the counting numbers in the channels with the strongest radiations from this isotope is utilized in a first embodiment for earth type correction, where the counting number Int is multiplied with the correction factor K/overK, which results in Int • K/overK where Int is the counting number in the energy range of 225 keN to 3045 keN, K is the counting number in the energy range of 1290 keN to 1590 keN, and overK is the counting number in the energy range of 1650 keN to 3045 keN. This embodiment ensures a considerable improvement compared to the total counting number alone, cf. Fig. 3, which clearly shows that the variation is reduced by a multiplication with the correction factor. The total counting number of the 20 earth samples examined showed a relative variation of 15%. It is possible to reduce the variation to 9.6% by means of the correction factor. Fig. 3 shows furthermore that after multiplication with the correction factor the earth samples 2, 5 and 13 are nevertheless placed considerably lower than the remaining samples. The samples 2, 5, and 13 are all types of humus. According- ly a correction for types of humus must be performed. It appears from Fig. 3, that the three types of humus do not differ essentially relative to one another. If humus can be identified, it must therefore be possible to compensate therefor. Experience has taught that potassium is less active in humus than in other types of earth. The relationship between the integrated counting number in the low energy range (150 to 450 KeN) divided by the counting number in the potassium range (1290 to 1590 keN) provides therefore a good indication of whether the earth contains humus. The above locations of the two energy ranges (windows) result in a limit of about 3.85. When the relationship between the countings in the two ranges, i.e. 540 to 630 KeN and 1290 to 1550 KeN, exceeds 3.85, the sample must be considered containing humus. On the other hand when the rela¬ tionship is lower than 3.85, it is a question of other types of earth. By such an indication, uranium is an important factor because uranium decays to Bi-314 producing a strong peak with a centre in 609.3 KeN. A high counting number in this range can be due to a high content of uranium. A correction for types of humus is performed by means of a soft step function of the formula f(x)=l + h - h/(exp a (x - g)) + 1) illustrated in Fig. 8. This function is advantageous in changing from the value 1 to the level 1 + h when h is the difference between the level before and after the change, X Q is the centre of the change, and a is a constant determining the narrowness of the change interval. Together with the limit of 3.85 this function is used to separate humus from the remaining types of earth so as to compensate for humus. The total correction factor to be multiplied with Int is [1 + h - h/(exp(a(x - Q )) + 1)] K/overK The constants have been found by way of tests and are h = 0,35 a = 20 XQ = 3,o5. This embodiment has been tested on 20 types of earth, and the variation divided by the average number is 4.6%. Thus the variation has been considerably re¬ duced. Example This example deals with three different types of earth. The sample numbers are 2: humus/clay 7: sand 15: heavy clay. The spectrum of energy of these three types of earth appears from Figs. 4 to 6. The counting numbers are as follows: calculated values. ... Int • K/overK W200/W480 Correction factor Comp. • Int • K/overK It appears that sample No. 2 is a type of humus. Despite the different types of earth, the deviation from the highest value 65690 for sample No. 15 to the lowest value 59848 for sample No. 7 amounts only to 9.2% of the average value. When this embodiment is used on the 20 samples of earth, the variation of the results is reduced to 4.6% of the average value. Fig. 7 illustrates the following for all 20 samples of earth the sum of the countings from the energy range 225 keV to 3045 keV - the sum of the countings corrected by Int • K/overK the sum of the countings corrected by K/overK and by the correction for humus. The variation of the results is acceptable. A demand exists for a higher counting number in all energy ranges, as the neces¬ sary measuring time would thereby be reduced. A higher counting number can be obtained by summing up over large intervals of the spectrum or by placing the windows in which said summing up is performed in intervals presenting a higher counting number per channel. It appears from the above table that the lowest counting numbers are found in the window "overK". This window cannot be extended as it would then be influenced by the radiation from potassium. Accor¬ dingly another embodiment must be developed which only utilizes windows in the range from and including potassium and further down. Here it is possible to utilize that uranium and thorium also emit quanta of lower energies during their decay. A correction for humus according to such an embodiment renders it pos¬ sible to reduce the measuring period. The factor W 470 2 /W87 acts like Int • K/overK which means that the relative variation of the measurings is almost the same on the 20 samples after the correc¬ tion by means of this factor because said factor (the correction factor) also pres¬ ents low values for humus. W470 is the potassium peak and W87 is the sum of the channels covering energies from keN 225 to 300 keN. In this range Ac - 228 (daughter of Thorium-232) and Ra - 226 (daughter of uranium-238) are found. The range is furthermore influenced by secondary absorptions on other isotopes, which results in a slight blurring of the radiations from uranium and thorium. W 470 2 /W87 is of the same nature as Int • K/overK because the potassium window has apparently more weight than in the previous embodiment when W470 is raised to the 2nd power. The effect of uranium and thorium is, however, moder- ated as the counting numbers of the high energies are not "pure", but instead W87 from very low energies also depending on other conditions. Example of attenuation of γ-radiation in a load of beets. m R is the mass of clean beets in the load N is the volume of the entire load (a constant) J% is the earth percentage calculated at m j /m R In other words, the earth percentage is calculated as a percentage of the clean beets and not as a percentage of the total mass. The density of clean beets in the load is therefore: The density of the entire load is determined by The density of the earth alone in the volume of the entire load is J%m R PJ = —^ = M»PR p B representing the density of attenuating material, and p j representing the den¬ sity of γ-radiating material. The area of a spherical shell of a radius r is found at 4 r 2 Δr. The volume of a spherical shell of the thickness Δr is approximately ΔN = 4τrτ 2 Δr The mass of radiating material in this spherical shell is then Δm = ΔNp j = 4τrr 2 p J Δr The number of transmitted quanta from the mass Δm in the period Δt is Δ__ g = E Q ΔmΔt, where E Q is the counting number from the earth measured by the detector per time unit and per mass unit of earth. E^ depends on the detector. At the distance r from the earth with the mass Δm and during the period Δt the following unattenuated signal is measured by the detector: Δ/ n Δ ( ) = the solid angle "seen" by a radiation-transmitting element being inversely propor¬ tional to the square on the distance. This signal is attenuated across the distance to the detector. This distance is r-r 0 , where r 0 is the radius of the detector. The measured signal is consequently: where μ is the coefficient of absorption. μ = ln(2)/d , where d^ is the halving thickness. It is assumed that the halving thickness is inversely proportional to the density of the attenuated material: d, Λ = C/p B = > μ = ln(2) B /C = C IPB , = ln(2)/C After insertion in the above formula the following result is obtained: and by inserting the expression for ΔI Q the following is obtained Δt -MM . ^ ^'^ By inserting the expression forΔm the following is obtained = > ΔI 2 (r) = 4xp J E 0 Δte- c 1 V r - r 0 >Δr Furthermore the densities can be substituted with the result ΔI 2 (r) =4τr %p R E 0 Δte: c 1 < , R (1 + J%) ) Ar When the thickness of the spherical shell goes to zero, the formula is as follows: In order to find the total radiation, an integration is performed over all extremely thin spherical shells from 0 to r: I 2 (r)= J 4xJ% r R E 0 Δte- c 1 R (1 - +J%)(r - dr r 0 By K-* = 4ττJ%p R E 0 Δt, and K 2 = C j p R (l +J%), the following is obtained r 0 As a result: = ^l ( 1 - e -^-'-o ) ) - or with K ! and K 2 inserted: Example of measuring heavy clay and humus, respectively. The example includes two measurings on materials being admixed 20% of earth, where both measurings involve a measuring period of 500 sec. Example 1 - heavy clay The dry matter content in the earth is set to 80.2%, the reason why the measur¬ ably earth percentage is 16.0%. Based on the spectrum resulting from the mea- suring the following values are found: Channels Energy range counting number [keN] W87 [75-99] [225-297] 11358 W470 [420-519] [1260-1557] 3278 W200 [140-240] [420-720] 0146 The result is W470 2 /W87 = 946,05 This number is proportional to the attenuated earth percentage. In order to con¬ vert into attenuated earth percentage, a division by a proportionality factor Ju is performed, said factor Ju being found by way of tests to be 6810, and the follow¬ ing value is obtained Attenuated earth percentage = 13,89% Now a correction is performed for the attenuation caused by the yet unknown earth percentage, which results in a measured earth percentage of 13.89%. For this purpose the following formula is used: / = 4π %E θΔ f (1 _ e -C, Pfl <1 ♦Λ)(r-r 0 H 2 C,(1 + %) 1 In this formula I 2 is the measured earth percentage and J% is the unknown unattenuated earth percentage. The constants are Eo = 7,19775xl0 "7 m 2 /(kg s) Δt = 500 s p R = 700 kg/m 3 C λ = 0.0045 m 2 /kg = ln(2)/(d 4 p B ) r-r 0 = 1,50 m The iteration results in J% = 16,1 %. This earth percentage has not been corrected for humus. The integral W200 is known and the following number is found W200/W470 = 3,095 This number is inserted in the correction function for humus: HK M 0 _- λ + H - H W470 F M ∞ _a e W470 where H = 0,35 F = 27 S = 3,4875 The correction function for humus is shown in Fig. 8. When the present value is inserted, the result is: H/C(3,095) = 1 +0,35- 0,35 e 27(3,095-3,4875)^ = 1 ,000 This function value is multiplied with the earth percentage, which in this case causes no change as the earth type is heavy clay. Then the earth percentage is 16,1%. This is very close to the admixed amount when a correction for water content is performed. Example 2 - humus. In this case 20% of humus has been admixed. The dry matter content in the earth sample was 68,5% which corresponds to a measurable earth percentage of 13.7%. The spectrum of this measuring appears from Fig. 2. The counting numbers are: W87 10202 W470 2499 W200 9472 The channel numbers and energies are as stated in Example 1. W470 2 /W87 = 612,1 612,1/Ju = 612,1/6810 = 0,089 = 8,99% The correction for attenuation is found by iteration to 0,099 = 9,9%. W200/W470 = 9472/2499 = 3,790 results in 0,35 HK(3,790) = 1 +0,35- -= 1 ,350 27(3,790-3,4875)^ If should be noted that a fiill reflection of humus is given here. The function value is multiplied with the resulting earth percentage: 1,350 x 9,9% = 13,4%, which deviates 0,3% from the true value.

Claims: Claims. 1. A method of detecting the earth content in agricultural crops, such as beets, by measuring the γ-radiation of the earth, the counting number of the measured γ-radiation being corrected for differences in different types of earth, char- acterised bythe counting number being corrected for the content in the earth of humus by utilizing that the content of humus is the primary factor influ¬ encing the counting number, 2. A method as claimed in claim 1, characterised by correcting for the content of humus in the earth by compensating for the content of potassium in the earth by utilizing that humus contains a particularly high amount of ura¬ nium compared to the amount of potassium. 3. A method as claimed in claim 2, characterised in that the correc¬ tion for the content of potassium is performed by the counting number Int of the measured γ-radiation being corrected for by the factor K/overK, where Int is the counting in almost the entire energy range, K is the counting in the range con¬ taining the highest amoimt of potassium, and overK is the counting in the energy range thereabove. 4. A method as claimed in claim 2, characterised in that a correction is instead performed by the factor W470 2 /W87, where W470 is the counting in the range 1260 to 1557 keN, and W87 is the counting in the range 225 to 297 keN. 5. A method as claimed in one or more of the preceding claims, charac¬ terised in that a further correction is performed for types of humus by means of a step function preferably presenting a soft transition. 6. A method as claimed in claim 5, characterised in that the step function with the soft transition is of the formula f(x) = 1 + h - h/(exp(a (x - X Q )) + 1), where h is the step size, X Q is the point of change, and a is a constant determin¬ ing the narrowness of the change range.

Inventors: FRYDENDAL IB, HANSEN OLE, JORGENSEN LARS BO, THOMASSEN JESPER, FRYDENDAL, IB, HANSEN, OLE, JORGENSEN, LARS, BO, THOMASSEN, JESPER
Applicants: DANISCO, FRYDENDAL IB, HANSEN OLE, JOERGENSEN LARS BO, THOMASSEN JESPER, DANISCO A/S, FRYDENDAL, IB, HANSEN, OLE, JORGENSEN, LARS, BO, THOMASSEN, JESPER
Application year: 1994
Main classification: G01N33
IPC codes: G01N23, G01N33